1. Field of the Invention
The present invention relates to a link type variable stroke engine, and especially relates to a link type variable stroke engine in which, in a crankcase of an engine main body, a crankshaft is rotatably supported, and a rotary shaft is rotatably supported so that power reduced at a speed reduction ratio of ½ from the crankshaft is transmitted thereto, the rotary shaft having an axis parallel with the crankshaft and being provided with an eccentric shaft at an eccentric position, and a piston, slidably fitted to a cylinder block of the engine main body, the crankshaft and the eccentric shaft are linked by a linking mechanism, the linking mechanism including: a main connecting rod coupled, at one end, with the piston by using a piston pin; a sub connecting rod rotatably coupled with a crank pin of the crankshaft and rotatably coupled with the other end of the main connecting rod; and a swing rod rotatably coupled, at one end, with the sub connecting rod at a position displaced from a position coupled with the main connecting rod and rotatably coupled, at the other end, with the eccentric shaft.
2. Description of the Related Art
In a conventional reciprocating engine, inertial exciting force, which induces inertial vibration, occurs at two parts: a reciprocating part including a piston and a small end of a connecting rod; and a rotating part including a crank pin and a big end of the connecting rod. To suppress and lessen the exciting force, counterweights are generally provided on a crankshaft so that centers of gravity of the counterweights are located on the opposite side of the axis of the crankshaft from the crank pin and on a straight line connecting the axis of the crankshaft and the axis of the crank pin.
Meanwhile, a link type variable stroke engine has already been known by Japanese Patent Application Laid-open No. 2000-73804 and the like. In the link type variable stroke engine, a piston, a crankshaft and an eccentric shaft are linked by a linking mechanism, the eccentric shaft provided to a rotary shaft which is parallel with the crankshaft and to which power reduced at a speed reduction ratio of ½ from the crankshaft is transmitted. Even in such a link type variable stroke engine, inertial exciting force needs to be suppressed and lessened.
In the link type variable stroke engine, inertial exciting force occurs due to a lumped mass near a connecting rod pin rotatably connecting a sub connecting rod with a main connecting rod, a lumped mass near a swing pin connecting the sub connecting rod with a swing rod and a lumped mass near the eccentric shaft, besides the inertial exciting force occurring due to the mass of a reciprocating part, which is the mass of the entire piston and a one-end-side part of the main connecting rod, and the mass of a rotating part, which is the mass of a crank pin and the mass of a part of the sub connecting rod near the crank pin. Accordingly, the inertial exciting force unique to the link type variable stroke engine cannot be effectively reduced with the same configuration as that of the reciprocating engine, that is, the configuration in which counterweights, are provided so that centers of gravity of the counterweights are located on the opposite side of the axis of the crankshaft from the crank pin and on a straight line connecting the axis of the crankshaft and the axis of the crank pin as shown in Japanese Patent Application Laid-open No. 2000-73804.
For this reason, when the inertial exciting force becomes excessively large and consequently the inertial vibration becomes large, a worker using an apparatus equipped with the link type variable stroke engine, for example, a working machine, feels uncomfortable, the working machine starts to move by itself and thereby grounding performance is deteriorated, and noise attributable to vibration increases, for example. Moreover, an excessive increase in the inertial exciting force may also cause a reduction in the strength of components of the engine.